Electrical conduit is normally coupled by sleeve couplings. Where threaded couplings are employed, they are customarily threaded for a single direction of rotation, e.g. right-hand threading. Reverse threading is known, as for use in turn buckles. The use of right hand and left-hand threading in conduits, particularly in an explosion-proof environment for the purpose of locating and supporting parts, is believed not to have been previously contemplated.
U.S. Pat. No. 4,454,376 is of interest as it shows an electrical connector with reverse threads at each end. This is not however, the same as a conduit, and not a conduit that serves to support other parts. It is, therefore, not in the class of the present invention.
Threaded couplings are used for electrical conduit in explosion-proof equipment because it has been established that a series of consecutive threads provides a flame path of adequate length and/or gap to serve as a barrier against the propagation of a flame. Thus if a flammable gas is ignited by an electrical spark within a conduit, the resulting flame cannot spread to the outer atmosphere.
For explosion-proof electrical equipment, it is typically necessary to run conductors from one location to another. It is also desirable to provide junction boxes for the joining of conductors. When such a junction box is mounted externally, the conductors leading to it must be contained within conduits.
This invention is particularly suited to the coupling of conduit leading to a junction box in such an environment.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.